The present invention relates to the general field of thrusters or rocket engines for delivering thrust for driving vehicles such as missiles, launchers, or indeed satellites, using the principle of propulsion by reaction or by ejecting gas. The invention relates more particularly, but not exclusively, to nozzles fitted to solid propellant thrusters.
A solid propellant thruster is constituted mainly by a shell containing a block of propellant, an igniter, and a nozzle having a stationary diverging portion. The block of propellant is pierced by a channel situated on the axis of the thruster and that serves as a combustion chamber. The igniter ignites the propellant at one end of the shell and combustion of the propellant propagates from the front towards the rear of the thruster. The propellant burns at a predefined speed producing combustion gas, which is expelled through the nozzle.
The throat section of the nozzle serves to regulate the combustion of the block of propellant so as to maintain the desired pressure inside the combustion chamber while also producing the expected thrust. Furthermore, for a thruster that delivers thrust at a single rate, the throat section of the nozzle is single and predetermined as a function of the desired thrust level.
Nevertheless, having recourse to a single throat section is not appropriate for a thruster that has two operating rates, typically operation at a high rate (acceleration) and operation at a low rate (cruising), or for a thruster that is designed to fly at varying altitudes.
To mitigate such a drawback, one known solution consists in providing the launcher with two distinct thrusters: one for the acceleration (or “boost”) stage and another for the cruising stage. Nevertheless, such a solution has the drawback of significantly increasing the cost of the launcher.
It is also known to provide a nozzle with a throat section that is variable. In practice, a plug that is movable in translation is housed inside the nozzle. The position of the plug in the flow of combustion gas serves to determine the flow section of the gas leaving the nozzle, thereby adjusting the gas ejection section to the operating rate of the thruster.
Nevertheless, known positioning systems associated with a movable plug are systems that are complex and expensive, and that significantly increase the mass of the thrusters.
There exists a need to modulate the ejection section of a nozzle in a manner that is inexpensive and capable of optimizing the thrust coefficients and to do so while minimizing the size and the mass of the modulation device in the thruster.